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AST 101 Introduction to Astronomy: Stars & Galaxies

AST 101 Introduction to Astronomy: Stars & Galaxies

AST 101 Introduction to : & REVIEW and Deat of High Stars (M > 8 Msun)

Last stage:

Iron core surrounded by shells of increasingly lighter elements.

REVIEW • When mass is too large (>1.4Msun), core collapses and get compressed into pure

• + à neutrons +

• Eventually degeneracy pressure stops the collapse abruptly

• Infalling atmosphere impacts on the core and bounces back [recall demo from last class]

Te ’s former surface zooms outward wit a velocit of 10,000 km/s! “Massive Star ”

• Exploding remnant of massive star disperses heavy elements through the

• Inside may be a – a remnant core of pure neutrons!

Crab (M1), first seen as SUPERNOVA on 4 July 1054 from China -- visible in daytime Was Crab SN recorded in Chaco?

• Petroglyph from Chaco Canyon (New Mexico): – Correct configuration relative to the new for the Crab Supernovae – Of course it could also just be Venus with the moon!

• Chinese records also report a “” in the sky in 1054 A.D. Observing Supernovae

• About 1 per century per galaxy (none in since 1604) L

• Bright explosions visible for weeks/months – some visible in daytime!

• Remnant visible for 100’s of thousands of years as huge bubbles and “veils” Supernovae in Other Galaxies

• Bright enough to be seen as a sudden, bright point in other galaxies

• Scores of amateur and pro monitor nearby galaxies nightly to catch them – (1 per 100 years per galaxy means that monitoring 100 galaxies will get you 1 supernova per year) SN 1987A: Nearest One Since 1604

• Exploded in the (companion dwarf galaxy to MW, 150,000 ly away)

• Seen only from southern hemisphere – But detectors in Ohio, Japan, and Russia detected neutrinos from the explosion!

• Ring structure: illuminated remnants of an earlier or gas left over from star’s formation (In ) Is Currently In Its Supergiant Phase

might be next…

only 1500 ly away.. would be very dramatic… REVIEW The ultimate fate of a massive star Core burns to Fe, leading to a core collapse SUPERNOVA

What happens to the Fe core?

Neutron Star - for star < 30-40 Msun

Black Hole - for star masses > 30-40 Msun The Stellar Graveyard REVIEW What’s In The Stellar Graveyard?

• Low mass stars (M< Msun) à white dwarfs – Gravity vs. electron degeneracy pressure

• High mass stars (M>8Msun but M<30-40Msun) à neutron stars – Gravity vs. neutron degeneracy pressure

• Even more massive stars (M> 30-40Msun)à black holes – Gravity wins Clicker Question

When a high-mass star (M>8Msun)ends its life, what does it leave behind?

A. A neutron star or B. A dwarf C. A black hole D. A neutrino ball E. A red supergiant Clicker Question

When a high-mass star (M>8Msun)ends its life, what does it leave behind?

A. A neutron star or black hole B. A C. A black hole D. A neutrino ball E. A red supergiant Clicker Question

Binary Systems: The Paradox

• Algol is a binary system consisting of a 3.7 star and a 0.8 solar mass . Why is this strange?

• A. A 3.7 MSun star should have become a red giant before a 0.8 MSun star • B. Binary stars usually have the same mass

• C. 0.8 MSun stars usually never become red giants Clicker Question

Binary Systems: The Algol Paradox

• Algol is a binary system consisting of a 3.7 solar mass main sequence star and a 0.8 solar mass red giant. Why is this strange?

• A. A 3.7 MSun star should have become a red giant before a 0.8 MSun star • B. Binary stars usually have the same mass

• C. 0.8 MSun stars usually never become red giants Algol Binary System

• Binary stars can have different masses but usually ARE formed at the same time.

• More massive star should have had a shorter main sequence lifetime What happened? early MS Binary Mass Exchange 3.0 1.5 • The 0.8 solar mass star once was more massive (3.0), with a 1.5 mass companion -2.2

• As it became a red giant, it swelled and poured material onto its companion (lost 2.2)

• The red giant (0.8) is now now 0.8 3.7 less massive than its companion (3.7)

• Future: when the other star becomes red giant, it may pour gas back…? Moral of the story: Choose your companions wisely, for they may determine your fate White Dwarfs in Binary Systems • from a companion red giant spirals into an disk

• Inner parts become VERY hot; glow in UV (mostly), X-rays Novae (not Supernovae!)

• Accretion of gas onto the white dwarf can and fuse into for a while (only on surface)

• Star becomes much brighter à (new star) – Dimmer than supernova but still impressive! White Dwarf Supernovae

• If enough mass is accreted, degeneracy is overcome – Limit = 1.4 Solar masses (recall the ) • Star then collapses, fusion begins in its core (explosively) Dr. Chandrasekhar says: “Do not weigh more than – Bye bye white dwarf! 1.4 solar masses or you will collapse!” Comparing The Two Types of Supernovae

• Massive star SN (collapse of massive star) – Found in young regions – Make neutron stars or black holes

• White dwarf SN (flash burning of WD) – Binary systems only – Occurs in older star populations – Nothing left inside We’ll be looking at these again as distance measurement tools! Comparing Three Types of Stellar Explosions • White – Binary systems only – Occurs in older star populations – White dwarf still survives • White Dwarf Supernova – Binary systems only – Occurs in older star populations – Nothing left inside • Massive Star Supernova – Found in young star formation regions – Make neutron stars or black holes Clicker Question

Where is fusion happening in a nova?

A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a nova, the comes from the collapse (and bounce) of the star. Clicker Question

Where is fusion happening in a nova?

A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a nova, the light comes from the collapse (and bounce) of the star. Clicker Question

Where is fusion happening in a white dwarf supernova?

A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a white dwarf supernova, the light comes from the collapse (and bounce) of the star. Clicker Question

Where is fusion happening in a white dwarf supernova?

A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a white dwarf supernova, the light comes from the collapse (and bounce) of the star. Clicker Question

Where is fusion happening in a massive star supernova?

A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a massive star supernova, the light comes from the collapse (and bounce) of the star. Clicker Question

Where is fusion happening in a massive star supernova?

A. In the core, carbon is being fused into heavier elements. B. On the surface, hydrogen is being fused into helium. C. No fusion occurs in a massive star supernova, the light comes from the collapse (and bounce) of the star. Since white dwarfs in evolving binary systems come “alive” – what about neutron stars?

Binary WD: Hot accretion disks, novae, supernovae

Neutron star: with more vigor, no SN MASS TRANSFER Neutron Stars in Binary Systems

• Mass transfer builds very hot around neutron star: à intense x-ray emission (continuosly) from disk à explosive helium burning (in bursts) on NS = X-ray Burster à falling in can “spin up” the neutron star (or ) QUIZ #4

a) Describe how a Nova is produced [3pt] b) Describe how a White Dwarf Supernova is produced [3pt] c) Describe how a Massive Star Supernova is produced [3 pt] d) What is the compact object left behind a low-mass star?

(M< 8 Msun) [1pt]

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